Hypothalamic–pituitary–thyroid axis

thyroid homeostasis or thyrotropic feedback control) is part of the neuroendocrine system responsible for the regulation of metabolism and also responds to stress.

The major portion of T3, however, is produced in peripheral organs, e.g. liver, adipose tissue, glia and skeletal muscle by deiodination from circulating T4.

Recent research suggested the existence of an additional feedforward motif linking TSH release to deiodinase activity in humans.

[6][7][8] The existence of this TSH-T3 shunt could explain why deiodinase activity is higher in hypothyroid patients and why a minor fraction of affected individuals may benefit from substitution therapy with T3.

[18] Recent research suggests that ghrelin also plays a role in the stimulation of T4 production and the subsequent suppression of TSH directly and by negative feedback.